[LLVMdev] Expand vector type

Martinez, Javier E javier.e.martinez at intel.com
Tue Feb 28 16:27:14 PST 2012


My input language has support for 3 and 4 element vectors but my target only has support for the latter. The language defines vec3 with the same storage space as vec4 so from a backend perspective they are both the same. I'd really like if I could have LLVM treat vec3 as vec4 but I haven't found out how.

Currently the target has emulated support for vec3 through LLVM. Loads are already widened by LLVM to a vec4. Stores are kind of funny. By default LLVM sets the action to 'widen' but in GenWidenVectorStores what ends up happening is an 2:1 split of the vector that's less efficient in this case than actually widening the vector. The reason is that at this point the call to FindMemType assumes that stores can never be widened to a bigger type and so those types are not considered. The call sequence I'm looking at is WidenVectorOperand() -> WidenVecOp_STORE() -> GenWidenVectorStores() -> FindMemType(). I've made a very small modification to enable support for widening stores to a larger type.

Before spending more time on working on a generic solution I have a couple of questions:
* Is there a way to setup LLVM to automatically convert vec3s to vec4s?
* Is there interest in adding support for widened vector stores to a larger type?

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